In this project the synthesis and characterization of the complexes with possible bio- and electro- or photochemical applications have been discussed. ( 1 ) [Co(bnzacdien)(bzlan)]ClO 4 ( 2 ) [Co(bnzacdien)(mrpln)]BPh 4 ( 3 ) [Co(bnzacdien)(prldn)]BPh 4 ( 4 ) [Co(bnzacdien)(pprdn)]BPh 4 ( 5 ) [Co(bnzacdien)(py)]BPh 4 ( 6 ) [Co(bnzacdien)(3-Mepy)]BPh 4 ( 7 ) [Co(bnzacdien)(4-Mepy)]BPh 4 ( 8 ) [Co(bnzacdien)(N-MeIm)]BPh 4 The complexes, ( 1 ) to ( 8 ) are synthesized in good yield and are characterized by FT-IR, UV-Vis and 1 H-NMR spectroscopy and elemental analyses. The structure of complex ( 1 ) have been determined by X-ray crystallography, and the correlation between structural and spectroscopic properties are discussed. It seems that the pentadentate ligand is coordinated unsymmetrically to the cobalt centre. Therefore the methyl groups on the imine carbon of the pentadentate ligand appear as tow separate singlets in the 1 H-NMR spectrum. The steric effects on the structural properties of these complexes are discussed and compared with those of similar complexes that have been reported. The electrochemical properties of complexes ( 1 ), ( 2 ), ( 5 ), ( 7 ) are also studied by Cyclic Voltammetery. The results show that the reduction of Co(III) to Co(II) is irreversible and there is no direct correlation between the redox potentials and the pK a of axial amines and these potentials are dependent on structural effects.